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P. Young, E. Mamajek, D. Arnett, J. Liebert (Steward Observatory, The University of Arizona)
We present comparisons between the detached, double-line eclipsing binaries of Andersen (1991), which have precisely determined masses and radii, and stellar evolution models produced with the TYCHO code. A set of eighteen binary systems were chosen which cover a range of mass from 22.89 to 0.96 Msol. The error of the models in Teff, luminosity and the time difference (between the best fit models for each member of a pair) had dispersions of ~ 3%, 6%, and 10%, respectively, without optimization of parameters. This indicates that the contributions to observable parameters from poorly constrained (either theoretically or observationally) effects such as abundances, rotation and convective overshooting are of order a few percent for the majority of stars. The outlying stars provide candidates for observations which may shed light on these effects.
Pre-MS models matched EK Cep B, a known post-T Tauri star and the PV Cas system, comprised of peculiar late B/early A stars which have historically proven difficult to fit (Pols et al., 1997). Estimates of the time until Roche lobe overflow identified five systems which may begin mass transfer when < 10% older than their current age. The primary of zeta Phe in particular appears to be especially close to Roche lobe overflow, which may explain the difficulty in fitting conventional stellar models to the system. Finally, the structural k constants were calculated from the best fit models for a subset of eleven systems with published apsidal motions.
This work was supported in part by the DOE, grant number DE-FG03-98DP00214/A001.